This application claims the benefit of Korean Application No. 2001-27486 filed May 19, 2001, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of and apparatus for detecting a reproduction signal from an optical disc having a varying track width.
2. Description of the Related Art
Recordable optical discs, such as a CD-R, a CD-RW, a DVDxe2x88x92RAM, a DVDxe2x88x92R, a DVDxe2x88x92RW, and a DVD+RW, have a guide groove along their tracks to enable an optical pickup to accurately track a desired track. A region of the optical disc with the guide groove is referred to as a xe2x80x9cgroovexe2x80x9d and a remaining region is referred to as xe2x80x9clandxe2x80x9d. Recording methods of such optical discs are classified into methods of recording user data on either land or grooves of the optical disc as in the CD-R/RWs, the DVDxe2x88x92R/RWs and the DVD+RW, and methods of recording user data on both land and grooves of the optical disc as in the DVDxe2x88x92RAM.
In manufacturing groove tracks and/or land tracks of recordable optical discs, a wobble signal for controlling a rotational speed of an optical disc and providing synchronization (sync) information is recorded by using a variation in a direction of amplitude of the wobble signal.
In addition, physical identification data (PID), such as sector address information, for indicating a physical location on an optical disc, is recorded on the optical disc in the manufacturing process. PID is recordable on an optical disc by a method of adding a PID signal to a wobble signal or by a method of forming uneven pre-pits in a header region or land of the optical disc.
A PID addressing method using a wobble signal, frequency or phase modulation of a wobble involves recording address information by adding frequency or phase variation in a predetermined period to a single-frequency wobble signal. A PID signal recorded overlapping the wobble signal is called a xe2x80x9cwobble addressxe2x80x9d.
As is known in the field to which the present invention pertains, CD-R/RW type optical discs record address information by frequency modulation of a wobble period, whereas DVD+RW type optical discs record address information by phase modulation of wobble. For both CD-R/RW and DVD+RW type optical discs, user data are recorded in only groove tracks so that PID addressing is achieved by forming a frequency-modulated or phase-modulated wobble on both sidewalls of each groove track.
In contrast, for land/groove-recordable optical discs such as a DVDxe2x88x92RAM in which user data is recordable in both land and groove tracks, it is impossible to realize PID addressing by merely forming a frequency-modulated or phase-modulated wobble on both sidewalls of each groove track. Thus, address information is recorded by forming uneven pre-pits in the header region of the disc. The PID addressing method using pre-pits has a problem of decreasing a recording capacity of the disc because user data cannot be recorded in the pre-pits region.
To maximize the recording capacity of land/groove-recordable optical discs, there is a need to increase a recordable region (user data region) by minimizing an overhead region (non-recording region), as well as to reduce a track pitch.
A wobble signal, which controls the rotational speed of the optical disc and provides sync information, is recorded in such land/groove-recordable optical discs. But it is not possible to record a PID signal to overlap the wobble signal in the land/groove-recordable optical disc by a known wobble addressing method.
Referring to FIG. 1, the PID addressing method using a wobble signal is based on variation in the amplitude of a wobble in a target groove track. Thus, where wobble address information with respect to each groove track is recorded along both sidewalls of each groove track, address information recorded in two groove tracks adjacent to a land track is simultaneously read in a land track so that address information with respect to the land track is not accurately detected. Address information for both land and groove tracks is not represented with wobble address formed in groove tracks.
To solve the above-described problems, it is an object of the present invention to provide a method of and apparatus for reproducing data recorded on an optical disc in which an excellent reproduction signal is detectable during reproduction from the optical disc where the optical disc has a varying track width, particularly, a land/groove-recordable optical disc in which a wobble address for a land track is recorded by quadrature phase shift keying (QPSK) modulation.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects of the present invention, there is provided a method of detecting a reproduction signal from an optical disc, comprising: dividing a light beam reflected from a recording surface of the optical disc into a central light beam portion and outer light beam portions in a direction corresponding to a radial direction of the optical disc, detecting the divided central light beam and outer light beam portions, and outputting a first detection signal from the central light beam portion and a second detection signal from at least one of the outer light beam portions; adjusting an amplitude of at least one of the first detection signal and the second detection signal; and detecting a reproduction signal by subtraction between an adjusted first detection signal and the second detection signal, the first detection signal and an adjusted second detection signal, or an adjusted first detection signal and an adjusted second detection signal.
To further achieve the above and other objects of the present invention, there is also provided an apparatus for detecting a reproduction signal from an optical disc, comprising: a light beam division and detection unit which divides a light beam reflected from a recording surface of an optical disc into a central light beam portion and outer light beam portions in a direction corresponding to a radial direction of the optical disc and detects the central light beam and outer light beam portions; and a signal processor which adjusts an amplitude of a first detection signal from the central light beam portion and/or an amplitude of a second detection signal from at least one of the outer light beam portions and detects a reproduction signal by subtraction between the first detection and second detection signals having the adjusted amplitudes.
In the method and apparatus described above, the method and apparatus are operable to detect a reproduction signal from an optical disc having a guide groove formed to track a desired track and a track whose width varies according to the structure of the guide groove, wherein a phase-modulated wobble signal including address information is recorded along a track, and wobble signals recorded in two adjacent groove tracks have a predetermined phase relation, thereby enabling addressing of a land track interposed between the two adjacent groove tracks. The method and apparatus are also operable to detect address information modulated by bi-phase shift keying (BPSK) and recorded in the groove tracks of the optical disc, wherein the wobble signals recorded in the two adjacent groove tracks have a phase difference of 90xc2x0 so that address information modulated by quadrature phase shift keying (QPSK) is recorded in the land track of the optical disc.
Preferably, the method and apparatus are operable to detect a reproduction signal where a wobble whose phase with respect to sine function is modulated by 0xc2x0 and 180xc2x0 is formed on both sidewalls of a predetermined guide groove and a wobble whose phase with respect to sine function is modulated by 90xc2x0 and 270xc2x0 is formed in a guide groove adjacent to the predetermined guide groove so that the width of a track interposed between the guide grooves varies.
Preferably, the method and apparatus are operable to detect a reproduction signal where the optical disc is a land/groove-recordable optical disc in which a wobble address is recorded and to detect a reproduction signal where a wobble is formed on only one of the sidewalls of the guide groove.
Preferably, the light beam division and detection unit divides the light beam reflected from the recording surface of the optical disc so that the central light beam portion corresponds to 10-90% of the diameter of the light beam.
Preferably, the light beam division and detection unit comprises a photodetector having a central light receiving section and outer light receiving sections arranged in a direction corresponding to the radial direction of the optical disc, wherein the central light receiving section receives the central light beam portion and the outer light receiving sections receive the outer light beam portions.
Preferably, the signal processor comprises: at least one gain controller which adjusts the amplitude of the first detection signal and/or the second detection signal from at least one of the outer light beam portions; and a subtractor which performs subtraction between the adjusted first and/or second detection signals/signal and outputs a result of the subtraction.